Ticks are parasites that feed on the blood of humans and animals, using it as their sole source of food. Due to their lifestyle, ticks at each life stage transmit various tick-borne pathogens while feeding on their hosts. Unlike mosquitoes - another important group of pathogen-transmitting arthropods - ticks can feed on the same host for prolonged periods, which underscores the importance of tick mechanisms that inhibit or reduce the host's defence mechanisms and, consequently, allow the transmission of pathogens. This unique tick-host-pathogen triangle requires the involvement of various tick molecules to mediate interactions with both host and pathogen molecules at multiple levels. This review highlights the glycan molecules identified in various tick species that can trigger an immune response and thus primarily affect the interaction with the host. As the enzymes involved in Golgi-mediated glycan maturation differ between ticks, insects, and their vertebrate hosts, these differences contribute to the glycan profiles observed in ticks. These differences in glycan structures influence the interactions ticks have with their hosts and pathogens. On one hand, they may participate in molecular mimicry and mechanisms that lower the host's immune reaction, blood clotting, and other defence mechanisms due to their different structures, but on the other hand they may also trigger the host's defence mechanisms, such as participating in delayed red meat allergy and facilitating the transmission of pathogens. Tick glycobiology remains largely unexplored and deserves more attention, especially considering the potential of glycans and glycoproteins as targets for anti-tick vaccines.
Contreras M, Vaz-Rodrigues R, Mazuecos L, Villar M, Artigas-JerĂłnimo S, et al.
Parasites & vectors •
Alpha-Gal syndrome (AGS) is a tick-borne food allergy caused by IgE antibodies against the glycan galactose-alpha-1,3-galactose (α-Gal) present in glycoproteins and glycolipids from mammalian meat. To advance in the diagnosis and treatment of AGS, further research is needed to unravel the molecular and immune mechanisms underlying this syndrome. The objective of this study is the characterization of tick salivary components and proteins with and without α-Gal modifications involved in modulating human immune response against this carbohydrate. Protein and α-Gal content were determined in tick saliva components, and proteins were identified by proteomics analysis of tick saliva fractions. Pathophysiological changes were recorded in the zebrafish (Danio rerio) model after exposure to distinct Ixodes ricinus tick salivary components. Serum samples were collected from zebrafish at day 8 of exposure to determine anti-α-Gal, anti-glycan, and anti-tick saliva protein IgM antibody titers by enzyme-linked immunosorbent assay (ELISA). Zebrafish treated with tick saliva and saliva protein fractions combined with non-protein fractions demonstrated significantly higher incidence of hemorrhagic type allergic reactions, abnormal behavioral patterns, or mortality when compared to the phosphate-buffered saline (PBS)-treated control group. The main tick salivary proteins identified in these fractions with possible functional implication in AGS were the secreted protein B7P208-salivary antigen p23 and metalloproteases. Anti-α-Gal and anti-tick salivary gland IgM antibody titers were significantly higher in distinct saliva protein fractions and deglycosylated saliva group when compared with PBS-treated controls. Anti-glycan antibodies showed group-related profiles. Results support the hypothesis that tick salivary biomolecules with and without α-Gal modifications are involved in modulating immune response against this carbohydrate.
Vector-borne diseases (VBD) challenge our understanding of emerging diseases. Recently, arthropod vectors have been involved in emerging anaphylactic diseases. In particular, the immunoglobulin E (IgE) antibody response to the carbohydrate Galα1-3Galβ1-(3)4GlcNAc-R (α-gal) following a tick bite was associated with allergies to red meat, cetuximab, and gelatin. By contrast, an anti-α-gal IgM antibody response was shown to protect against mosquito-borne malaria. Herein, we highlight the interplay between the gut microbiota, vectors, transmitted pathogens, and the regulation of the immune response as a model to understand the protective or allergic effect of α-gal. Establishing the source of α-gal in arthropod vectors and the immune response to vector bites and transmitted pathogens will be essential for diagnosing, treating, and ultimately preventing these emerging anaphylactic and other vector-borne diseases.